1. Field of the Invention
The invention relates to an acoustic driver and applied thermoacoustic device, and particularly to a radial acoustic driver and applied thermoacoustic device.
2. Related Art
Micro thermoacoustic technology uses acoustic waves to promote active heat transfer to create a cooler environment and effectively transfer heat from a heat source to a larger and cooler space. Together with passive heat transfer equipment such as a heat sink or fan, the heat is more easily removed using this technology. The technology is not only useful for removing heat from electronic devices but also for precise temperature control.
The composition of a micro thermoacoustic device includes an acoustic driver, a resonance tube, a stack and two heat exchangers. The fundamental aspect of the micro thermoacoustic device is that the acoustic driver generates pressure fluctuation of standing wave in the resonance tube to work on the fluid therein. A working fluid in resonator tube is ideally compressed and expanded adiabatic. Those processes cause heat to be transferred from one end of stack to the other. Thus, the temperature gradient is formed along the stack, producing a cooling effect.
Generally, conventional thermoacoustic devices generate pressure fluctuation by the acoustic driver. There are two kinds of thermoacoustic devices: as shown in FIG. 1, one includes a cylinder type resonance tube1, a planer acoustic driver3 used to produce axial acoustic waves, a stack 5, and heat exchangers 7 and 9 located at the opposite sides of the stack 5; as shown in FIG. 2, the disc type thermoacoustic device includes a planer acoustic driver 2, which generates radial acoustic waves by the design of slabs 4. The ring type stack of the disc type thermoacoustic device can be assembled around the cylinder tube such that the cooling capacity is higher even if the stack has the same thickness. The greatest amplitude of the pressure wave occurs around the locations of acoustic driver and the anti-node of the wave. However, whether the cylinder type thermoacoustic device or the disc type thermoacoustic device is used, the properties of acoustic driver dominated the amplitude of pressure fluctuation.
Concerning the cooling capacity of the thermoacoustic device, cooling capacity and the amplitude is directly proportional to acoustic energy, increasing the input acoustic energy into the thermoacoustic device is the only way to increase the cooling capacity. However, the acoustic energy generated by the planer type acoustic driver is restricted by the property of the piezoelectricity material.
There are many researches make an effort on increasing the cooling capacity of thermoacoustic device. However, improvement is not clear in the field of micro drivers. Therefore there remains the problem of how to increase pressure fluctuation without increasing the consumption of energy.